The present invention relates to a device for lubricating a power gearbox having a variable orientation particularly for a convertible tilt-rotor aircraft.
In general, the device for lubricating a gearbox comprises, in particular:
lubricating means, for example pumps, which supply lubricant to at least one element of said gearbox (gears, bearings, etc) that needs to be lubricated; and
a collecting reservoir which collects the lubricant from said gearbox.
It is known that, in the case of a customary gearbox which has a constant orientation during time with respect to the elements and structure around it, for example the main gearbox of a helicopter, lubricant is returned to the collecting reservoir generally by no particular means, simply under the effect of gravity, the lubricant running down along the walls of the gearbox and being collected directly by said reservoir, an opening into which is provided in the lowermost part of the gearbox.
Of course, such a method of collection is possible only when the gearbox has a stable orientation so that the opening into the reservoir is then always situated vertically at the bottom of the gearbox, in the region where the lubricant accumulates.
By contrast, when the orientation of the gearbox varies, the region in which the lubricant accumulates in the gearbox also varies and tends to lie away from the entry into the collecting reservoir, so that this method of collection is then no longer appropriate.
This is why it is necessary to provide special-purpose collecting means in variable-orientation gearboxes, such as a main gearbox of an aircraft of the convertible tilt-rotor type. In an aircraft such as this which has vertical take-off in the manner of a helicopter, the rotors then acting as rotary wings, and which performs cruising flight in the manner of an airplane, the rotors operating in this case as propellers, there is generally provided, for transmitting power between each rotor and the motor associated with it, a transmission system comprising a tilting reduction assembly:
which is produced in the form of a gearbox;
which is connected to a non-tilting reduction assembly connected to a shaft of said motor; and
which drives said rotor.
In general, by way of special-purpose collecting means, use is made of a pump which pumps the lubricant from an accumulating region to the lubricating reservoir. Since, in this case (variable-orientation gearbox), there are at least two different accumulating regions, it is necessary to provide at least two pumps per transmission system (one for the airplane mode and one for the helicopter mode, in a convertible aircraft), and this leads to a significant increase in the mass and to reduction in reliability.
In addition, such a transmission system is complex and is difficult to maintain.
Furthermore, it is known that conventional pumps which are, for example, used in the gearboxes of a helicopter, cannot operate dry without sustaining damage. This is why the use of such pumps on a convertible aircraft poses serious reliability problems because in certain flight configurations, such as the helicopter mode, for example, the pumps designed for draining in the airplane mode are not supplied with lubricant or are supplied only intermittently.
It is an object of the present invention to overcome these drawbacks. The invention relates to a simple, lightweight and reliable device for lubricating a power gearbox which has variable orientation, particularly of a convertible tilt-rotor aircraft.
To this end, according to the invention, said lubricating device of the type comprising:
lubricating means for supplying lubricant to at least one element that needs to be lubricated of said gearbox comprising a closed space; and
a collecting reservoir for collecting the lubricant from said closed space,
is notable in that it additionally comprises:
at least one rotary drain screw, which is produced in the form of an Archimedian screw, equipped with a number of orifices and which is arranged in said closed space to convey lubricant from said closed space to said collecting reservoir; and
drive means for driving said drain screw in rotation,
and in that said orifices are made in the drain screw in an arrangement such that said drain screw can collect the lubricant from said closed space regardless of the orientation of said gearbox.
Thus, as use is simply made of an Archimedian screw for collecting the lubricant, said lubricating device becomes simpler to produce and simpler to maintain, and its mass and bulk are reduced.
In addition, unlike the aforementioned solutions, the Archimedian screw which, in the known fashion, comprises a helix rotating about its axis in a channel and which causes the lubricant to move along, can run dry, with an air/oil mixture, and can do so without the risk of cavitation.
Furthermore, by virtue of the invention, it is possible to use a very simple system for transmitting movement to the drain screw and for guiding its rotation. In particular:
the drain screw can take its movement (from the drive means) by way of a belt or a chain. As a preference, however, it does so by means of gears made of synthetic material, which have the advantage of being lightweight; and
guidance can be by means of plane bearings rather than rolling bearings.
Furthermore, advantageously, said drain screw is at least partially made of synthetic material, which makes it possible to reduce the mass and wear still further.
The present invention also relates to a transmission system for the transmission of power between a drive motor and a tilt rotor, which is capable of tilting between a first position in which it is capable of operating as a rotary wing, and a second position in which it is capable of operating as a propeller, said transmission system comprising a tilting reduction assembly:
which is produced in the form of a gearbox;
which is connected to a non-tilting reduction assembly connected to a shaft of said motor; and
which drives said rotor.
According to the invention, this transmission system is noteworthy in that said gearbox of the tilting reduction assembly comprises at least one lubricating device such as the aforementioned one according to the invention.
Furthermore, the present invention also relates to a convertible tilt-rotor aircraft capable of operating in airplane mode and in helicopter mode and comprising at least one fuselage, a fixed wing structure comprising at least two wings extending laterally one on each side of said fuselage and, in helicopter mode, a rotary wing structure comprising at least two rotors which in airplane mode act as propellers and each of which is mounted so that it can tilt on a respective fixed wing and is connected, by a respective transmission system, to a respective motor supported by the corresponding wing. According to the invention, at least one of said transmission systems is the aforementioned one according to the invention.